The present invention relates to a data recording device for cameras which has a light source incorporated therein and which is adapted to record on the film the desired data, such as the date of taking a photograph, and more particularly to a data recording device for use in a camera having an automatic focusing mechanism which emits a signal for actuating the device.
As disclosed in Japanese Utility Model Publication No. 15478/1975, conventional data recording devices for cameras are initiated into a data recording operation by a switch operatively associated with a specific mechanical movement, such as a shutter release action of the camera. The switch or like member needed for actuating the device renders the input assembly for the device complex in construction. Since the exposure for recording data generally requires a longer period of time than exposures for taking usual photographs owing to limitations on the size of the light source lamp, the capacity of the power supply battery and the optical system for the device, the recording device is provided with safety means for eliminating the likelihood that the film will be wound up before the completion of data recording operation. The safety device nevertheless makes the camera complex in construction and renders the camera unable to take photographs in succession at a high speed.
As disclosed in U.S. Pat. No. 4,025,931, other data recording devices are known which are actuated by an electric signal emitted by the control circuit for an electronic shutter, for example, by an electric signal for de-energizing a shutter closing electromagnet in the exposure controlling timer circuit, or by an electric signal momentarily available when a shutter release member returns. Although such devices have an input assembly of simple construction, data must be recorded on the film after the shutter has been closed but before the film is wound up. Otherwise, the data would be recorded on the film in the form of a blurred image. Accordingly the data exposure time is limited to a relatively short period of time. The data exposure time is still shorter with cameras provided with means for automatically winding up the film with earlier timing after the shutter has been closed. Such limitations on the data exposure time give rise to the necessity of passing a greater current through the light source lamp for data recording to give increased brightness to the lamp. A dash of increased current then flows through the lamp, recording the life of the lamp and the reliability of the device.
When a prolonged data exposure time is used to overcome the problem, a blurred data image will inevitably result depending on the film winding timing if the film is wound up automatically or even if it is wound manually. Alternatively there is the need to delay the film winding timing, but this entails difficulty in taking photographs with proper timing or in photographing a moving or changing subject in succession.
Furthermore, the data exposure time control electric circuit of the device includes many switches which function mechanically. Such mechanical switches not only make the device complex but also are costly because they require the use of expensive metal, such as platinum, which gives inproved corrosion resistance and enhanced reliability to the switches.
U.S. Pat. No. 3,953,868 discloses another device including a data exposure light source which is energized by closing the synchronization contact of the camera for firing flash bulbs. However, since the synchronization contact is closed when the shutter is fully opened, the data exposure time is limited to a relatively short period of time also in this case. The device therefore has the same drawback as the prior art described above.